Доклади на Българската академия на науките Comptes rendus de l’Acad´ emie bulgare des Sciences Tome 67, No 6, 2014 BIOLOGIE Biotechnologie BIODEGRADATION POTENTIAL OF NOCARDIA FARCINICA BN26 FOR XENOBIOTICS MINERALISATION Alexander Hristov, Nelly Christova, Lilyana Nacheva, Ivanka Stoineva * , Lyudmila Kabaivanova (Submitted by Corresponding Member O. Poljakova-Krusteva on March 6, 2014 ) Abstract In the present study the catabolic activity of the biosurfactant-producing strain Nocardia farcinica BN26 was followed to prove its potential for bioreme- diation. These bacteria were examined for their degradation ability by exposing them to different temperatures and 29 ◦ C was found as the optimum temper- ature. The rate of phenol mineralisation by the bacterium using different cell densities was also estimated. The adaptation capabilities of the bacterium in a semicontinuous process with multiple xenobiotic supply was studied. The cells that had undergone 10 passages on 500 mg/l phenol containing medium had the highest capacity for degrading both the aromatic and aliphatic xeno- biotics added at equal concentrations. During the biodegradation of the hy- drophilic and hydrophobic xenobiotics, the biosurfactant production increased up to 500 mg/l. A significant decrease of the surface tension to 32 mN/m was also registered, accompanied by decreased cell hydrophobicity (29%), in that way favouring the bioremediation process. Simultaneous biodegradation till total depletion of phenol (3.5 g/l) and n-hexadecane (0.5 g/l) for 18–24 h was established for the investigated strain. Key words: phenol, n-hexadecane, biodegradation, Nocardia farcinica Introduction. Aromatic compounds and aliphatic alkanes are often found together in different wastes [ 1 ]. The origin of phenols in the environment is both anthropogenic as well as xenobiotic. Phenols can come from several types of 821